Properly handle older GHC and container combinations

Two conflicting issues:

* cabal-install on Travis-CI was selecting newer versions of
  containers than shipped with the corresponding version of GHC (thus
  hiding the other issue).

* foldlWithKey' was added in containers-0.4.2, and thus not available
  in older versions.  We now fudge it with foldWithKey, which dates
  back to 0.1 (and thus always available).

Author: ivan-m

.travis.yml

@@ -11,13 +11,16 @@ before_cache:
   - rm -fv $HOME/.cabal/packages/hackage.haskell.org/build-reports.log
   - rm -fv $HOME/.cabal/packages/hackage.haskell.org/00-index.tar
 
+env:
+  global:
+    - CONF=""
+
 matrix:
-  fast_finish: true
   include:
-    - env: CABALVER=1.16 GHCVER=7.0.4
+    - env: CABALVER=1.16 GHCVER=7.0.4 CONF="-f -containers042"
       compiler: ": #GHC 7.0.4"
       addons: {apt: {packages: [cabal-install-1.16,ghc-7.0.4], sources: [hvr-ghc]}}
-    - env: CABALVER=1.16 GHCVER=7.2.2
+    - env: CABALVER=1.16 GHCVER=7.2.2 CONF="-f -containers042"
       compiler: ": #GHC 7.2.2"
       addons: {apt: {packages: [cabal-install-1.16,ghc-7.2.2], sources: [hvr-ghc]}}
     - env: CABALVER=1.16 GHCVER=7.4.2
@@ -56,11 +59,11 @@ install:
    fi
  - travis_retry cabal update -v
  - sed -i 's/^jobs:/-- jobs:/' ${HOME}/.cabal/config
- - cabal install --only-dependencies --enable-tests --enable-benchmarks --dry -v > installplan.txt
+ - cabal install --only-dependencies --enable-tests --enable-benchmarks $CONF --dry -v > installplan.txt
  - sed -i -e '1,/^Resolving /d' installplan.txt; cat installplan.txt
 
 # check whether current requested install-plan matches cached package-db snapshot
- - if diff -u installplan.txt $HOME/.cabsnap/installplan.txt;
+ - if diff -u $HOME/.cabsnap/installplan.txt installplan.txt;
    then
      echo "cabal build-cache HIT";
      rm -rfv .ghc;
@@ -86,7 +89,7 @@ install:
 # any command which exits with a non-zero exit code causes the build to fail.
 script:
  - if [ -f configure.ac ]; then autoreconf -i; fi
- - cabal configure --enable-tests --enable-benchmarks -v2  # -v2 provides useful information for debugging
+ - cabal configure --enable-tests --enable-benchmarks -v2 $CONF # -v2 provides useful information for debugging
  - cabal build   # this builds all libraries and executables (including tests/benchmarks)
  - cabal test
  - cabal check
@@ -96,7 +99,7 @@ script:
 # If there are no other `.tar.gz` files in `dist`, this can be even simpler:
 # `cabal install --force-reinstalls dist/*-*.tar.gz`
  - SRC_TGZ=$(cabal info . | awk '{print $2;exit}').tar.gz &&
-   (cd dist && cabal install --force-reinstalls "$SRC_TGZ")
+   (cd dist && cabal install --force-reinstalls $CONF "$SRC_TGZ")
 
 # Check the fgl-arbitrary sub-package
  - cd fgl-arbitrary
@@ -110,5 +113,4 @@ script:
  - SRC_TGZ=$(cabal info . | awk '{print $2;exit}').tar.gz &&
    (cd dist && cabal install --force-reinstalls "$SRC_TGZ")
 
-
 # EOF

Data/Graph/Inductive/PatriciaTree.hs

@@ -273,7 +273,7 @@ addLists xs  ys  = xs ++ ys
 
 addSucc :: forall a b . GraphRep a b -> Node -> Int -> IM.IntMap [b] -> GraphRep a b
 addSucc g0 v numAdd xs
-  | numAdd < bulkThreshold = IM.foldlWithKey' go g0 xs
+  | numAdd < bulkThreshold = foldlWithKey' go g0 xs
   where
     go :: GraphRep a b -> Node -> [b] -> GraphRep a b
     go g p l = IMS.adjust f p g
@@ -285,9 +285,19 @@ addSucc g v _ xs = IMS.differenceWith go g xs
     go (ps, l', ss) l = let !ss' = IM.insertWith addLists v l ss
                         in Just (ps, l', ss')
 
+foldlWithKey' :: (a -> IM.Key -> b -> a) -> a -> IntMap b -> a
+foldlWithKey' =
+#if MIN_VERSION_containers (0,4,2)
+  IM.foldlWithKey'
+#else
+  IM.foldWithKey . adjustFunc
+  where
+    adjustFunc f k b a = f a k b
+#endif
+
 addPred :: forall a b . GraphRep a b -> Node -> Int -> IM.IntMap [b] -> GraphRep a b
 addPred g0 v numAdd xs
-  | numAdd < bulkThreshold = IM.foldlWithKey' go g0 xs
+  | numAdd < bulkThreshold = foldlWithKey' go g0 xs
   where
     go :: GraphRep a b -> Node -> [b] -> GraphRep a b
     go g p l = IMS.adjust f p g

fgl.cabal

@@ -109,6 +109,11 @@ test-suite fgl-tests {
 }
 
 benchmark fgl-benchmark {
+    if flag(containers042)
+        buildable:    True
+    else
+        buildable:    False
+
     default-language: Haskell98
 
     type:             exitcode-stdio-1.0